1. Field of the Invention
The present invention relates to a device employing a ceramic superconducting element and, more particularly, to an improvement of a logic device and memory device which are controlled by the magneto-resistive characteristics of a ceramic superconducting device by the magnetic field change effecting to the superconducting element.
2. Description of the Prior Art
It is known to use the Josephson effect to theoretically form a logic circuit such as an AND gate. Josephson device is one of well-known logic devices which use the characteristics of superconductors. The logic device utilizing the Josephson effect, herein referred to as a Josephson device, according to prior art has a structure that an extremely thin insulation film is sandwiched between layers made of superconducting materials, such as niobium, lead, or their alloys.
The insulation film in a Josephson device of the above type requires a thickness on the order of ten angstroms. Production of such a thin insulation film, however, requires advanced thin film manufacturing technologies, and actual production is difficult. In addition, although one technical advantage of the Josephson device is its extremely fast operating speed, the output level change is very small. Thus, the Josephson device is not applicable to logic circuits from a practical viewpoint.
In view of the above, a ceramic superconducting element's new phenomenon has been found and is disclosed in detail in prior Japanese Patent applications No. 62-233369 et seq (corresponding to U.S. application Ser. No. 226,067 filed July 29, 1988, and to E.P. application No. 88307044.3 filed July 29, 1988), which is assigned to SHARP KABUSHIKI KAISHA, one of the co-assignee of the present application. When the ceramic superconducting element utilizing the new phenomenon is employed in a logic circuit, such as in an AND, OR, XOR (exclusive or), or NOT (inverter) gate, such a logic circuit shows a stable operation and can be manufactured at a high yield rate, as disclosed in Japanese Patent application No. 63-117472 (corresponding to U.S. application Ser. No. 289,312 filed Dec. 23, 1988, to E.P. application No. 88312296.2 filed Dec. 23, 1988, and to Chinese application No. 88109265.7 filed Dec. 24, 1988), and in Japanese Patent application No. 63-29526 (corresponding to U.S. application Ser. No. 309,228 filed Feb. 10, 1989, to E.P. application No. 89301279.9 filed Feb. 10, 1989, and to Chinese application (application number not yet received)) which are also assigned to SHARP KABUSHIKI KAISHA, one of the co-assignee of the present application.
Although these applications teach the use of the ceramic superconducting element in a logic circuit, such as in an AND, OR, XOR (exclusive or), or NOT (inverter) gate, none of these teaches or suggests the use of the same in a logic circuit which can perform the IMPLICATION or EQUIVALENCE gate operation. The following Tables A and B show the IMPLICATION and EQUIVALENCE logics when they are expressed by the truth table.
TABLE A ______________________________________ IMPLICATION Truth Table Input Output ______________________________________ 0 0 1 1 0 0 0 1 1 1 1 1 ______________________________________
TABLE B ______________________________________ EQUIVALENCE Truth Table Input Output ______________________________________ 0 0 1 1 0 0 0 1 0 1 1 1 ______________________________________
Also, these applications do not teach or suggest the use of the ceramic superconducting element in a memory device.
Furthermore, Josephson devices have been conventionally used for storing data by utilizing the characteristics of superconductivity. In such devices, the presence or absence of fluxoid quantum traveling through a loop connected to the Josephson device was correlated to storage states "1" and "0."
However, the structure of Josephson devices such as those used in conventional superconducting memory devices is typically layered, specifically one in which a thin film insulation layer is sandwiched between superconductor layers of niobium, lead, alloys thereof, or other materials.
In a Josephson device as described above, the interposed insulation film must be formed on the order of ten angstroms in order to achieve the tunnel effect enabling superconductivity. That production of such a thin insulation film, however, requires advanced thin film manufacturing technologies and actual production is difficult, that the output level is low, and that use is only possible at very low temperatures has prevented the practical application of such devices.